Agulhas Climate Modeling

Agulhas leakage, the warm and salty Indian ocean water that leaks into the Atlantic ocean, has potential climate impacts via modulating the meridional overturning circulation in the basin. Our work is among the first to study leakage using a fully-coupled climate model that capable of resolving the mesoscale dynamics in the Agulhas Current system (CCSM3.5 with 1/10 deg ocean resolution). We quantify Agulhas leakage by tracking Lagrangian particles, following a popular numerical recipe. We showed that the CCSM produces a more realistic mean leakage transport than its coarse resolution counterparts, and the standard-monthly outputs are sufficient to capture leakage variability at longer than seasonal time-scales. At inter-annual time-scales, we found that leakage is related to a meridional shift and/or strengthening of the westerlies, consistent with idealized simulations using OGCMs. Regionally, such variability is linked to several regional climate patterns including dipole structures in SST and surface heat fluxes, as well as reduced summer inland rainfall over southeastern Africa.